The present invention relates to the field of supplemental respiratory oxygen supply systems and methods. More particularly, the present invention provides methods and systems that conserve supplemental respiratory oxygen.
A large patient community is currently undergoing oxygen therapy at home or in long-term care facilities, such as nursing homes. Supplemental respiratory oxygen has been a widely accepted form of treatment for COPD (chronic obstructive pulmonary disease) patients with hypoxemia following the completion of a major National Institutes of Health study in 1980. The Nocturnal Oxygen Therapy Trial established the efficacy of continuous oxygen therapy in the extension of the life span of sufferers of COPD with chronic hypoxemnia.
For administration of long-term oxygen therapy it has been common practice to deliver the oxygen directly into the nostrils of the patient through a device known as a nasal cannula. The cannula is connected via a supply hose to a source of oxygen, such as an oxygen concentrator, liquid oxygen dewar or high pressure gas cylinder. The oxygen is delivered continuously to the patient at a rate prescribed by a physician.
It has been recognized that continuous oxygen delivery is wasteful of oxygen, as a patient needs oxygen only when they are inhaling and the oxygen delivered at other times is wasted. The most significant financial cost associated with this waste is found in the increased service visits required by the oxygen provider to replenish the patient""s oxygen supply, because the actual cost of the oxygen is only a small fraction of the total cost of the therapy.
Another problem associated with supplemental oxygen therapy is that the physical size and weight of the oxygen apparatus can reduce the patient""s mobility.
A number of approaches have been taken to address the problems of waste, cost and portability of oxygen therapy. The therapeutic approach that has grown out of this body of work is typically referred to as xe2x80x9cdemand delivery.xe2x80x9d The devices respond to a patient""s inspiratory effort by delivering a predetermined pulse of oxygen during the period of inhalation, rather than allow the oxygen to flow to the patient continuously. There are many ways in which this basic concept has been implemented.
Extensive work has been done on sensors, timing of oxygen release, and algorithms for delivery of the oxygen. A variety of methods for sensing the respiratory cycle have been used, including pressure sensors that are in fluidic communication with the patient""s airway, flow sensors, and chest belts which detect the movement of the thorax during respiration. Some systems deliver a small bolus of oxygen at the beginning of inhalation, while others deliver continuous flow throughout inhalation. There has also been work on the frequency of delivery. For example, some systems do not provide oxygen at every breath.
In spite of the large variety of approaches taken to conserve oxygen supplies and/or reduce the size and weight of the oxygen supply equipment, no consensus has yet been reached as to the most appropriate way to save oxygen and medicate the patient adequately.
The simplest approaches to conserve oxygen involve detection of inhalation as a trigger to deliver oxygen. A variety of detection devices were developed in pursuit of this basic approach to controlling oxygen supply, including a chest belt worn by the patient that generates an electrical signal to trigger the opening of the oxygen supply valve; a hand-activated breathing device attached to a portable gas bottle via a supply hose in which users would dispense the oxygen by pushing a button while holding the device next to their mouth; a mechanical chest strap/valve that functions as both an inhalation sensor and delivery device in an oxygen conserving system; and an all-pneumatic, fluidically-controlled device.
Another approach uses pressure sensors in the oxygen line to monitor line pressure at the nostrils. A small negative pressure, indicative of the onset of inhalation, triggers the release of oxygen. This type of detection scheme has become the standard method and is employed by most systems currently in use. The systems attempt to provide a physiologically equivalent dose of oxygen, when compared to continuous flow, by providing a burst of oxygen at the onset of inhalation. By providing more oxygen at the beginning of inhalation, when it is more physiologically useful, the most efficient of these systems claim to be able to reduce oxygen consumption.
The existing demand delivery devices provide economic benefit in the form of oxygen savings (and reduced service visits), but it is often at the expense of the level of medical care. In particular, some patients have been found to-have deficient levels of oxygen in their blood as a result of using known demand delivery devices. Certain activities, such as exercise and sleep, cause the body""s need for oxygen to fluctuate in an unpredictable manner. The chronic hypoxemia being corrected by the prescription of oxygen therapy is not fully ameliorated by these devices.
Because demand delivery devices and continuous flow systems do not measure the patient""s blood oxygen saturation, they do not respond to a change in patient need as would be indicated by a drop in oxygen saturation. The oxygen flow in the form of pulses of gas is fixed in some devices, such as the PulseDose by DeVilbiss, as it is delivered with every breath. In other devices, such as the Oxymatic 301 from Chad Therapeutics, the patient is allowed some adjustability in the flow by determining the frequency of pulses as a function of the number of breaths; i.e., one pulse every fourth breath, a pulse every other breath, etc. None of these types of demand delivery system is capable of directly addressing fluctuations in the blood oxygen level experienced by the user.
In fact, while it is generally known that existing modes of oxygen therapy are inadequate for most patients at least some of the time (that is, acute periods of hypoxia, SaO2 less than 88%, can be seen in virtually all patients for some fraction of each day), another problem that is not addressed by the known devices and methods is that the average COPD patient is receiving more oxygen than needed for a significant part of each day. For example, the oxygen patients studied by Decker, et al. (Chest 1992) had an SaO2 greater than 90% for more than 70% of the time they spent breathing room air without any supplemental oxygen. In another study of even sicker patients (Sliwinski, et al., European Respiratory Journal 1994), SaO2 was greater than 88% for 40% of the time while breathing room air, and greater than 92% (higher than necessary) for about 70% of the time they were using their supplemental oxygen. The lack of methods and/or systems for controlling the upper limit of blood oxygen content results in significant amounts of wasted oxygen.
Devices which control the flow of oxygen based on blood oxygen measurements from various types of sensors have been described for a variety of applications. However, none of these devices were meant for residential use by sub-acute COPD patients, none had the goal or object of conserving as much oxygen as possible while still maintaining a healthy blood oxygen level, and none used a pulsed, demand-delivery method for conserving oxygen.
Measurements of blood oxygen saturation can be broken into two groups of measurement strategies: invasive and non-invasive. An invasive measurement using existing technology requires that blood be drawn from the body and the sample placed in a blood gas analyzer. One common non-invasive blood oxygen sensor is a pulse oximeter which relies on the differences in the light absorption curves of saturated and desaturated hemoglobin in the infrared and near-infrared portions of the spectrum. The typical pulse oximeter sensor includes two LED""s, one red and one infrared. As the light from the two LED""s passes through a capillary bed at the point of attachment, such as is found on the finger, the light is partially absorbed by the blood and tissues and then is detected by a photodetector. The electrical signal generated by the photodetector, which is proportional to the amount of light absorbed by the body, is transmitted to the oximeter. The absorption measurements can be made rapidly, up to 500 times per second for each LED. Because of the pulsatile nature of arterial blood, the absorption as a function of time will vary slightly at the frequency of the pulse. This allows the oximeter to extract the arterial blood oxygen saturation information from background noise caused by absorption in tissues located between the LED""s and the photodetector. Pulse oximetry is a well-accepted technique and can be found in machines used for monitoring patients under anesthesia, patients participating in sleep studies and neonatal monitoring.
Some methods and systems for controlling oxygen delivery to patients in critical care settings have been disclosed. Some of the systems use feedback loop controllers that use the blood oxygen saturation signal, SpO2, from a pulse oximeter to control the inspired oxygen fraction (FIO2) in the respiratory gas delivered by a mechanical ventilator in which oxygen is mixed with air to supply an accurate amount of oxygen to a patient through a mask or hood. These systems are intended for the care of critically ill patients receiving treatment in hospitals for severe respiratory distress caused by a chronic condition or accident.
The present invention provides supplemental respiratory oxygen supply methods and systems which maintain healthy blood oxygen saturation in sub-acute patients receiving supplemental oxygen by controlling the dosing of oxygen with a measured response to the patient""s actual blood oxygen saturation levels. This closed-loop control of oxygen flow for COPD patients provides for both healthy blood oxygen levels and significant oxygen conservation by reducing or preventing the delivery of supplemental respiratory oxygen during those times when the patient has a desired blood oxygen level.
In one aspect, the present invention provides a method of controlling supplemental oxygen delivery during sub-acute care by continuously measuring blood oxygen content of a patient to obtain a measured blood oxygen content level; delivering supplemental oxygen from an oxygen source to the patient when the patient is inhaling if the measured blood oxygen content level is below a desired value; and restricting the delivery of supplemental oxygen if the measured blood oxygen content level of the patient is above the desired value.
In another aspect, the present invention provides a method of controlling supplemental oxygen delivery for sub-acute care by continuously measuring blood oxygen content of a patient to obtain a measured blood oxygen content level; sensing variations in respiration of the patient to determine when the patient is inhaling; delivering supplemental oxygen from an oxygen source to the patient through a supplemental oxygen delivery device when the patient is inhaling if the measured blood oxygen content level is below a desired value; and restricting the delivery of supplemental oxygen to the patient through the supplemental oxygen delivery device if the measured blood oxygen content level of the patient is above the desired value.
In another aspect, the present invention provides a method of controlling supplemental oxygen delivery for sub-acute care by continuously measuring blood oxygen content of a patient to obtain a measured blood oxygen content level; delivering a variable dose of supplemental oxygen from an oxygen source to the patient when the patient is inhaling, wherein the variable dose is at least partially determined based on the measured blood oxygen content level.
In another aspect, the present invention provides a method of controlling supplemental oxygen delivery for sub-acute care by continuously measuring blood oxygen content of a patient to obtain a measured blood oxygen content level; sensing variations in respiration of the patient to determine when the patient is inhaling; delivering a variable dose of supplemental oxygen from an oxygen source to the patient through a supplemental oxygen delivery device when the patient is inhaling, wherein the variable dose of supplemental oxygen is at least partially based on a difference between the desired value for the measured blood oxygen content level and the measured blood oxygen content level.
In another aspect, the present invention provides a method of sensing variations in respiration of a patient by providing a flow sensor in fluid communication with the respiratory flow of a patient; monitoring the flow sensor to determine when the patient is inspiring air; and monitoring the flow sensor to determine when the patient is expiring air.
In another aspect, the present invention provides a demand delivery method for controlling the delivery of oxygen to a patient by providing a flow sensor in fluid communication with the respiratory flow of a patient; monitoring the flow sensor to determine when the patient is inhaling; delivering oxygen to the patient when the patient is inhaling; monitoring the flow sensor to determine when the patient is exhaling; restricting delivery of oxygen to the patient when the patient is exhaling.
In another aspect, the present invention provides a system for delivering supplemental oxygen for sub-acute care, the system including a blood oxygen content level sensor; a source of supplemental oxygen; a valve in fluid communication with the source of supplemental oxygen; and a controller capable of operating the valve, the controller restricting flow through the valve when the blood oxygen content level measured by the blood oxygen content level sensor is above a desired value.
In another aspect, the present invention provides a system for controlling supplemental oxygen delivery including means for measuring blood oxygen content level of a patient; means for delivering supplemental oxygen from an oxygen source to the patient when the patient is inhaling if the measured blood oxygen content level is below a desired level; and means for restricting the delivery of supplemental oxygen from the oxygen source to the patient if the measured blood oxygen content of the patient is above a desired level.
In another aspect, the present invention provides a system for controlling supplemental oxygen delivery including means for measuring blood oxygen content level of a patient; and means for delivering a variable dose of supplemental oxygen from an oxygen source to the patient when the patient is inhaling, wherein the variable dose is at least partially determined based on the measured blood oxygen content.
As used in connection with the present invention, the terms xe2x80x9csupplemental oxygenxe2x80x9d and xe2x80x9csupplemental respiratory oxygenxe2x80x9d refer to oxygen delivered to patients in addition to the oxygen received by the patient through the inspiration of room or ambient air. Because room air contains some oxygen, the supplemental oxygen is provided in addition to the oxygen that would normally be inspired by the patient.
As used in connection with the present invention, the term xe2x80x9cblood oxygen contentxe2x80x9d and xe2x80x9cblood oxygen content levelxe2x80x9d will typically be used to refer to blood oxygen saturation as commonly measured by the percentage of oxygen-saturated hemoglobin (SpO2) although it can also refer to any suitable measurement for determining the level of oxygenation in a patient""s blood. For example, it will be understood that blood oxygen content can also be obtained based on data from a CO-oximeter. Furthermore, blood oxygen content, can also be obtained based on partial pressures of oxygen (PaO2).
As used in connection with the present invention, the term xe2x80x9csub-acute carexe2x80x9d refers to care provided to patients that is not intended to treat critical conditions. Typically, sub-acute care is provided to patients in residential settings. xe2x80x9cResidentialxe2x80x9d preferably includes, e.g., homes and long-term care facilities (such as nursing homes). Sub-acute care also includes care delivered in ambulatory situations, i.e., when the patient is engaged in normal activities outside of his or her residence, such as shopping, attending concerts or other events, traveling to appointments with health care professionals, etc.
As used in connection with the present invention, the terms xe2x80x9ccontinuousxe2x80x9d and xe2x80x9ccontinuouslyxe2x80x9d (when referring to the measuring of blood oxygen content levels) mean that the blood oxygen content level of the patient will be measured without cessation or at intervals (fixed or variable) that are sufficiently small to provide the advantages of the invention.
These and other features and advantages of the present invention will be apparent upon review of the detailed description of the invention and accompanying drawings.